In recent years, rechargeable secondary batteries have been widely used as energy sources for wireless mobile devices. In addition, the secondary battery is gaining attention as a power source of an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (Plug-In HEV), and the like, which are proposed as solutions for solving the air pollution of existing gasoline vehicles and diesel vehicles using fossil fuels.
Such a secondary battery is roughly classified into a cylindrical battery, a prismatic battery and a pouch-shaped battery according to the external and internal structural characteristics. Among them, a prismatic battery and a pouch-shaped battery which can be laminated with a high degree of integration and have a width smaller than the length have attracted particular attention.
The electrode assembly of the anode/separation membrane/cathode structure constituting the secondary battery is largely divided into a jelly-roll type (wound type) and a stacked type (laminated type) depending on its structure. In the jelly-roll type electrode assembly, an electrode active material or the like is coated on a metal foil used as a current collector, dried and pressed, cut into a band shape having a desired width and length, and a cathode and an anode are separated by means of a membrane using a separation membrane and are spirally wound to manufacture the same. Although such a jelly-roll type electrode assembly can be preferably used for a cylindrical battery, when applied to a prismatic or pouch-type battery, there is a problem that local stress is concentrated and the electrode active material is peeled off or the battery is deformed due to repeated shrinkage and expansion phenomenon during charge/discharge processes.
On the other hand, the stacked electrode assembly has a structure in which a plurality of anode and cathode unit cells are sequentially laminated, and there is an advantage in that it is easy to obtain a prismatic shape. However, there is a disadvantage in that a manufacturing process is cumbersome and the electrode is pushed when the impact is applied, causing a short circuit.
In order to solve such a problem, some prior art has developed an electrode assembly of advanced structure which is a mixed type of the jelly-roll type and the stacked type, wherein a full cell of an anode/a separation membrane/an cathode structure of a certain unit size or a bicell of an anode(cathode)/a separation membrane/a cathode(anode)/separation membrane/anode(cathode) structure was used to develop a stack/folding type electrode assembly of a structure folded by using a long length continuous separation film.
However, it is necessary to arrange the unit cells in a long sheet-like separation membrane one by one, and an internal space or a system for a manufacturing process such as holding and folding the unit cells and the separation membrane at both ends is indispensably required. The processing is very complicated, and the equipment investment cost is high as a result. Furthermore, as the unit cells increase, the unit cells are arranged in a line and are difficult to be wound, resulting in a problem that the defective rate of the electrode assembly may increase.